Groundwater is a key water source for hundreds of millions of people in Africa, but a growing demand for it means that researchers must keep track of the supply to make sure it doesn’t get depleted. To accurately estimate the future supply, the researchers fitted low-cost monitors on hand pumps across Kenya that measure the vibrations produced when water is being drawn from the Earth. They found that the vibrations reflect how deep the water supply is, and with hundreds of monitors in different locations in Kenya, they can finally predict the groundwater supply with accuracy. With such a desperate need for stable water sources, this technology can be key in ensuring water security.